Data transfer apparatus, data transmitting and receiving apparatus, and image forming apparatus

ABSTRACT

A data transfer apparatus includes a transmitting unit, a transmission controlling unit, and a generating unit. The transmitting unit transmits transmit data over a transmission channel having a plurality of lines, such that the transmit data are assigned to the plurality of lines by information unit of the transmit data, the information unit. The transmission controlling unit appends control data to transfer data to be transferred to a receiving side to compose the transmit data, the control data being for controlling transmission and reception of the transfer data. The generating unit obtains information about the number of the lines. The generating unit determines, based on the number of the lines and the number of information units of the control data, the number of information units of the transfer data that makes the number of information units of the transmit data integral multiple of the number of the lines.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims priority under 35 USC 119 fromJapanese Patent Application No. 2010-025472, filed Feb. 8, 2010.

BACKGROUND Technical Field

The present invention relates to a data transfer apparatus, a datatransmitting and receiving apparatus, and an image forming apparatus.

SUMMARY OF THE INVENTION

According to an aspect of the invention, a data transfer apparatusincludes a transmitting unit, a transmission controlling unit, and agenerating unit. The transmitting unit transmits transmit data over atransmission channel having a plurality of lines, such that the transmitdata are assigned to the plurality of lines by information unit of thetransmit data, the information unit including a plurality of pieces ofbit information. The transmission controlling unit appends control datato transfer data to be transferred to a receiving side to compose thetransmit data, the control data being for controlling transmission andreception of the transfer data. The generating unit obtains informationabout the number of the lines in the transmission channel. Thegenerating unit determines, based on the number of the lines and thenumber of information units of the control data, the number ofinformation units of the transfer data that makes the number ofinformation units of the transmit data integral multiple of the numberof the lines. The generating unit generates transfer data of thedetermined number of information units from a part of the transfer datato be transferred to the receiving side.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will be described in detail basedon the following figures, wherein:

FIG. 1 is an overall view of an image forming system according to afirst exemplary embodiment of the present invention;

FIG. 2 is a diagram showing a hierarchical structure of communicationperformed by a data transfer apparatus according to the first exemplaryembodiment of the present invention;

FIG. 3 is a diagram showing exemplary configurations of packetsaccording to the first exemplary embodiment of the present invention;

FIG. 4 is a diagram for explaining an example of a data transmissionmethod according to the first exemplary embodiment of the presentinvention;

FIG. 5 is a diagram showing an example in which a transmit data unit isassigned to a plurality of lanes, according to the first exemplaryembodiment of the present invention; and

FIG. 6 is a diagram showing an example in which a transmit data unit isassigned to the plurality of lanes, which is a comparative example.

DETAILED DESCRIPTION First Exemplary Embodiment

FIG. 1 is a diagram showing an image forming system according to a firstexemplary embodiment to which are applied a data transfer apparatus, adata transmitting and receiving apparatus, and an image formingapparatus of the present invention.

This image forming system 100 includes a computer 101 having inputdevices such as a keyboard 102 and a mouse 103; a display apparatus 104,such as a liquid crystal display, which is connected to the computer101; and an image forming apparatus 1 connected to the computer 101through a communication line 105 such as a LAN (Local Area Network).

The computer 101 is configured to be able to transmit an image data unitwhich is generated by a user operating the keyboard 102 and the mouse103, to the image forming apparatus 1 through the communication line105.

(Configuration of the Image Forming Apparatus)

The image forming apparatus 1 includes an I/F (Interface) unit 10, acontroller 11, a storage unit 12, an image forming unit 13, a paperfeeding unit 14, and a transmission channel 20 having a first lane to afifth lane 201 to 205 which are an example of a plurality of lines. Apart of the controller 11 and a part of the image forming unit 13configure a data transmitting and receiving apparatus 2 that transfersdata units from the controller 11 to the image forming unit 13. Notethat although here the controller 11 and the image forming unit 13 arepresent in the same apparatus, the configuration is not limited thereto.

The I/F unit 10 is configured by a circuit that receives informationtransmitted from the computer 101 through the communication line 105 andconverts the information into a signal format that is readable by thecontroller 11.

The controller 11 is configured by a circuit having a CPU forcontrolling the operation of each unit of the image forming apparatus 1,etc. The controller 11 includes a writing unit 111 that writes an imagedata unit inputted through the I/F unit 10 into the storage unit 12; areading unit 21 which is an example of a generating unit that reads apart of the image data unit from the storage unit 12 and therebygenerates a transfer data unit; an image data controlling unit 110 thatcontrols the operations of the writing unit 111 and the reading unit 21;a transmission controlling unit 22 that appends control data units forcontrolling transmission and reception of the transfer data unit, to thetransfer data unit generated by the reading unit 21 and thereby composesa transmit data unit; and a transmitting unit 23 that transmits thetransmit data unit such that the transmit data unit is assigned to thefirst to fifth lanes 201 to 205 in the transmission channel 20 in unitsof information, each of which includes a plurality of pieces of bitinformation. The reading unit 21, the transmission controlling unit 22,and the transmitting unit 23 are an exemplary configuration of the datatransfer apparatus 3.

As used herein, the term “units of information” refers to a unit used totreat a plurality of pieces of bit information as a unity. In thepresent exemplary embodiment, data including 8-bit information, bytedata, is described as one information unit but data including 16-bitinformation, word data, or information including 32-bit information,double word data, may be treated as one information unit.

The storage unit 12 is, for example, an SRAM, a DRAM, or an HDD. Thestorage unit 12 is configured to be connected to the writing unit 111and the reading unit 21 in the controller 11 to be able to store thewhole image data.

The image forming unit 13 is an example of the receiving side thataccepts transfer of an image data unit from the controller 11, and hasan output unit 130 that forms an image according to the image data uniton printing paper (not shown) contained in the paper feeding unit 14.The paper feeding unit 14 is configured to supply sheets of printingpaper one by one to the output unit 130 in the image forming unit 13.

(Configuration of the Data Transfer Apparatus)

The data transmitting and receiving apparatus 2 includes the readingunit 21, the transmission controlling unit 22, and the transmitting unit23 which are provided in the controller 11, a receiving unit 24 and areception controlling unit 25 which are provided in the image formingunit 13, and the transmission channel 20 having the first to fifth lanes201 to 205 provided between the controller 11 and the image forming unit13. Note that the number of a plurality of lanes included in thetransmission channel 20 may be an odd number other than 5 or an evennumber.

The reading unit 21 is configured to obtain information about the numberof lanes in the transmission channel 20 from the image data controllingunit 110, determine the number of bytes of a transfer data unit thatmakes the number of bytes of a transmit data unit an integral multipleof the number of lanes, based on the number of lanes and the number ofbytes of control data units which are appended by the transmissioncontrolling unit 22, and read a data unit of the determined number ofbytes from an image data to be transferred to the image forming unit 13and thereby generate a transfer data unit.

Specifically, the reading unit 21 reads, chunk by chunk, from thestorage unit 12, an image data unit of such a number of bytes that isobtained by subtracting the number of bytes of control data units whichare appended by the transmission controlling unit 22, from a value thatis an integral multiple of the number of lanes in the transmissionchannel 20 (five in the present exemplary embodiment), and therebygenerates transfer data units for a plurality of transmissions. A dataunit read by the reading unit 21 at a time is a data unit of a pluralityof bytes which is one of chunks into which the image data unit isdivided. The reading unit 21 generates a read data unit which is read ata time from the storage unit 12, as a transfer data unit to betransferred to the image forming unit 13.

The transmission controlling unit 22 appends control data unitsincluding a plurality of byte data units for controlling transmissionand reception of a transfer data unit, before and after the transferdata unit generated by the reading unit 21, as a transmit data unit tobe transmitted over the transmission channel 20, and thereby composesthe transfer data unit and the control data units appended to thetransfer data unit.

The transmitting unit 23 has an 8B10B converting unit 231 and aparallel/serial converting unit 232. The 8B10B converting unit 231converts a transmit data unit from an 8-bit data unit to a 10-bit dataunit. The parallel/serial converting unit 232 converts the 10-bit dataunit converted by the 8B10B converting unit 231 into a serial signal.

In addition, the transmitting unit 23 transmits the transmit data unitin units of bytes to the receiving unit 24 in the image forming unit 13by serial communication through the first to fifth lanes 201 to 205.Each of the first to fifth lanes 201 to 205 is configured to transmit atransmit data unit in units of bytes, whereby transmission of aplurality of byte data units is performed in parallel.

The receiving unit 24 receives the transmit data unit transmitted fromthe transmitting unit 23 over the transmission channel 20. The receivingunit 24 has a serial/parallel converting unit 242 and an 8B10B inverseconverting unit 241. The serial/parallel converting unit 242 convertsthe received data unit into a parallel signal. The 8B10B inverseconverting unit 241 inversely converts the 10-bit data unit convertedinto the parallel signal by the serial/parallel converting unit 242,into an 8-bit data unit.

The reception controlling unit 25 has an extraction function ofextracting the transfer data unit from the transmit data unit, based onthe content of the control data units included in the transmit data unithaving been subjected to serial/parallel conversion and 8B10B inverseconversion by the receiving unit 24; and a determination function ofdetermining whether there is an error, such as a communication error, inthe transmit data unit by analyzing the content of the control dataunits. The reception controlling unit 25 is configured to request thetransmission controlling unit 22 to retransmit the transmit data unitover the transmission channel 20 if it is determined by thedetermination function that there is an error, and to pass the extractedtransfer data unit to the output unit 130 if it is determined that thereis no error.

The output unit 130 stores transfer data units transferred from thecontroller 11 to the image forming unit a plurality of separate times.After all data units required to recompose the image data unit arecollected, the output unit 130 combines the stored transfer data unitsto recompose the image data unit, and forms an image according to theimage data unit on printing paper.

The reading unit 21 obtains number-of-lane information A which is usedto compute the number of bytes of a transfer data unit, from the imagedata controlling unit 110 and determines the number of bytes M of atransfer data unit by the following expression, using the number oflanes in the transmission channel 20 and the number of bytes B ofcontrol data units which are appended by the transmission controllingunit 22:M=A×N−B  (1)where N is a positive integer greater than or equal to (B/A).

When the value of the integer N is increased, the ratio of a transferdata unit to a transmit data unit increases and accordingly transferdata transmission efficiency increases; however, when a communicationerror occurs and thus the transmit data unit is retransmitted, itrequires a long time to retransmit the data unit. On the other hand,when the value of the integer N is reduced, the ratio of a transfer dataunit to a transmit data unit decreases and accordingly transmissionefficiency decreases. It is desirable to set the integer N such that thenumber of bytes M is, for example, between 300 bytes to 1000 bytes. Forexample, when the number of lanes A is 5 and the number of bytes B ofcontrol data units is 28 bytes, if the integer N is set to 108, then thenumber of bytes M is 512.

Note that, when the number of lanes through which data units aretransmittable from the transmitting unit 23 on the side of thecontroller 11 differs from the number of lanes through which data unitsare receivable by the receiving unit 24 on the side of the image formingunit 13, the image data controlling unit 110 provides information aboutthe smaller number of lanes to the reading unit 21.

(Hierarchical Structure of Communication Functions)

FIG. 2 is a diagram showing the communication functions of thetransmission controlling unit 22, the transmitting unit 23, thereceiving unit 24, and the reception controlling unit 25 in the form ofa hierarchical structure.

FIG. 3 is a diagram showing a structure of a transmit data unit which istransmitted from the transmitting unit 23. The hierarchical structureand the transmit data structure conform to the PCI Express standard.

The communication function of the transmission controlling unit 22includes a transaction layer 221, a data link layer 222, and a physicallayer 223. The transmitting unit 23 is configured as a port 230 having adifferential transmission circuit, etc., included in the physical layer223.

The communication function of the reception controlling unit 25 includesa transaction layer 251, a data link layer 252, and a physical layer253. The receiving unit 24 is configured as a port 240 having adifferential reception circuit, etc., included in the physical layer253.

The transaction layers 221 and 251 have packet assembly and disassemblyfunctions. As shown in FIG. 3, the transaction layer 221 of thetransmission controlling unit 22 appends a header 221 a of 12 bytes or16 bytes before a transfer data unit 21 a obtained from the reading unit21 and appends a 4-byte ECRC (End-to-End Cyclic Redundancy Check) dataunit 221 b after the transfer data unit 21 a, and thereby constructs aTransaction Layer Packet (TLP) 221A. The header 221 a is datarepresenting the packet characteristics of the TLP such as header lengthand priority. The ECRC 221 b is data for detecting an error in data by acyclic redundancy check.

The data link layers 222 and 252 play a main role in ensuring theintegrity of the data units of the transaction layer packet 221A byerror detection and correction (retransmission), and further mutuallyperform packet exchange for flow control, etc. The data link layer 222of the transmission controlling unit 22 further appends a 2-bytesequence number 222 a before the transaction layer packet 221A andappends a 4-byte LCRC (Link Cyclic Redundancy Check) data unit 222 bafter the transaction layer packet 221A, and thereby constructs a datalink layer packet 222A. The sequence number 222 a is data representingthe order of transmission of the TLP, and the LCRC 222 b is data for acyclic redundancy check by the data link layer.

The physical layers 223 and 253 have circuits required forcommunication, such as a driver and a buffer. The physical layer 223 ofthe transmission controlling unit 22 further appends a 1-byte startframe 223 a before the data link layer packet 222A and appends a 1-byteend frame 223 b after the data link layer packet 222A, and therebyconstructs a physical layer packet 223A. The physical layer packet 223Acorresponds to a transmit data unit.

A control data unit 220A including the start frame 223 a, the sequencenumber 222 a, and the header 221 a, and a control data unit 220Bincluding the ECRC 221 b, the LCRC 222 b, and the end frame 223 b areexamples of control data units for controlling transmission andreception of the transfer data unit 21 a. In the example shown in FIG.3, the number of bytes of the control data units 220A and 220B is 24bytes (when the header 221 a has 12 bytes) or 28 bytes (when the header221 a has 16 bytes).

The reception controlling unit 25 processes the transmit data unittransmitted from the transmitting unit 23 in the order of the physicallayer 223, the data link layer 222, and the transaction layer 221 andextracts the transfer data unit 21 a, excluding the control data unitsappended by the transmission controlling unit 22. If an error in cyclicredundancy checks or sequence number inconsistency is found, then thereception controlling unit 25 requests the side of the controller 11 toretransmit the transmit data unit.

Each of the first to fifth lanes 201 to 205 in the transmission channel20 is a set of pairs of differential signal lines of, for example, 0.8volts, including a pair of signal lines on the transmitting side and apair of signal lines on the receiving side. Each of the first to fifthlanes 201 to 205 is configured to be able to perform not only datatransfer from the controller 11 to the image forming unit 13 but alsodata transmission from the image forming unit 13 to the controller 11.The transmission channel 20 which puts the first to fifth lanes 201 to205 together corresponds to a “link” in the PCI Express standard.

(Functions of the Transmitting Unit and the Receiving Unit)

FIG. 4 is a diagram showing the functions of transmitting and receivinga transmit data unit by the transmitting unit 23 and the receiving unit24. In the drawing, the first 1 byte of a transmit data unit isrepresented by “Sd0” and subsequent bytes of the transmit data unit arerepresented by “Sd1”, “Sd2”, . . . . For example, when the transmit dataunit shown in FIG. 3 is transmitted, the start frame 223 a correspondsto “Sd0” and the sequence number 222 a corresponds to “Sd1” and “Sd2”.

The transmitting unit 23 is configured as follows. Specifically, whenthe transmitting unit 23 starts transmission, the transmitting unit 23assigns the first 5-byte data units (“Sd0” to “Sd4”) of a transmit dataunit to the first to fifth lanes 201 to 205, respectively. Then, the8B10B converting unit 231 performs 8B10B conversion on the byte dataunits. Furthermore, the parallel/serial converting unit 232 converts thebyte data units to serial data units. Then, the serial data units aretransmitted through the first to fifth lanes 201 to 205 by serialcommunication. As used herein, the term “8B10B conversion” refers to theconversion of an 8-bit byte data unit to a 10-bit data unit where thereare less consecutive “0s” or “1s”. The 8B10B conversion is performed toprevent a cross point between differential signals which serve asreference signals for generating a clock used to detect a signal by thereceiving unit 24, from existing for a long period of time.

After the transmitting unit 23 assigns the first 5-byte data units(“Sd0” to “Sd4”) of the transmit data unit to the first to fifth lanes201 to 205, the transmitting unit 23 assigns 5-byte data units (“Sd5” to“Sd9”) subsequent to the first 5-byte data units to the first to fifthlanes 201 to 205, respectively. The data units assigned to the lanes 201to 205, respectively, are subjected to 8B10B conversion andparallel/serial conversion and then sequentially transmitted. Thetransmitting unit 23 is configured to repeatedly perform conversion andtransmission on a 5-byte basis until transmission of all the data unitsof the transmit data unit is completed.

The receiving unit 24 is configured as follows. Specifically, thereceiving unit 24 receives 10-bit data units transmitted through thefirst to fifth lanes 201 to 205. Then, the serial/parallel convertingunit 242 converts the data units to parallel data units. The 8B10Binverse converting unit 241 inversely converts each of the parallel dataunits from a 10-bit data unit to an 8-bit byte data unit. Furthermore,the converted byte data units are recombined to reproduce the transmitdata unit.

The reception controlling unit 25 extracts a transfer data unit from thereproduced transmit data unit and passes the transfer data unit to theoutput unit 130. The output unit 130 is configured to recompose an imagedata unit generated by the computer 101, based on transfer data unitsand form an image according to the image data unit on printing paper.

(Operation of the Image Forming System)

Next, the operation of the image forming system 100 will be describedwith reference to FIGS. 1 to 6.

When a user operates the keyboard 102 and the mouse 103 to allow thecomputer 101 to create an image and then provides an instruction toprint the image by, for example, operating the mouse 103, the computer101 transmits information representing the image created by the user, asan image data unit, to the image forming apparatus 1 through thecommunication line 105.

The I/F 10 in the image forming apparatus 1 receives a transmit signalfrom the computer 101, converts the signal into a signal format that isreadable by the controller 11, and outputs the signal. The controller 11obtains the image data unit through the I/F 10 and the writing unit 111stores the image data unit in the storage unit 12. The number of bytesof the image data unit is 1 megabyte in the case of, for example, an A4size, 24-bit color image.

When the image data unit is stored in the storage unit 12, the imagedata controlling unit 110 in the controller 11 instructs the readingunit 21 to read the image data unit from the storage unit 12. At thistime, the image data controlling unit 110 provides information about thenumber of lanes in the transmission channel 20 (five in the presentexemplary embodiment) to the reading unit 21.

The reading unit 21 obtains the information about the number of lanes inthe transmission channel 20 from the image data controlling unit 110.Then, the reading unit 21 reads from the storage unit 12 an image dataunit of such a number of bytes that is obtained by subtracting thenumber of bytes of control data units which are appended by thetransmission controlling unit 22, from a value that is an integralmultiple of the number of lanes, and thereby generates a transfer dataunit. The reading unit 21 performs the process of reading the image dataunit from the storage unit 12 a plurality of separate times such thatthe image data unit is divided into chunks of such a number of bytesthat is determined based on the aforementioned expression, untilcompleting the reading of all the image data unit; generating transferdata units for such a number of transmissions that corresponds to thenumber of the readings; and sequentially passing the transfer data unitsto the transmission controlling unit 22.

Then, as shown in FIGS. 2 and 3, the transmission controlling unit 22appends control data units including a header 221 a, an ECRC 221 b, asequence number 222 a, an LCRC 222 b, a start frame 223 a, and an endframe 223 b, to each transfer data unit by the processes of thetransaction layer 221, the data link layer 222, and the physical layer223.

Subsequently, as shown in FIG. 4, the transmitting unit 23 assigns atransmit data unit including a transfer data unit and control data unitsappended to the transfer data unit, to the first to fifth lanes 201 to205 in units of bytes, performs 8B10B conversion and parallel/serialconversion on the transmit data unit, and transmits the convertedtransmit data unit.

At this time, the number of bytes of the transmit data unit is the sum(M+B) of the number of bytes M read by the reading unit 21 at a time andthe number of bytes B of the control data units, and is equal to theproduct of the number of lanes A and the integer N (M+B=A×N). Therefore,there is no need to transmit unnecessary data units to some of the lanesand transmission of the transmit data unit completes by N transmissions.

The receiving unit 24 receives the data units transmitted through thefirst to fifth lanes 201 to 205, performs serial/parallel conversion bythe serial/parallel converting unit 242 and 8B10B inverse conversion bythe 8B10B inverse converting unit 241 on the data units, and passes thedata units to the reception controlling unit 25.

The reception controlling unit 25 performs cyclic redundancy checksbased on the ECRC 221 b and the LCRC 222 b and a sequence numberconsistency check based on the sequence number 222 a after receiving thewhole transmit data. If there is no error, then the receptioncontrolling unit 25 extracts the transfer data unit from the transmitdata unit. If there is an error, then the reception controlling unit 25requests the transmission controlling unit 22 to retransmit the transmitdata unit over the transmission channel 20. In response to the request,the transmission controlling unit 22 retransmits the transmit data unit.

The output unit 130 obtains transfer data units from the receptioncontrolling unit 25 and stores the transfer data units. After all dataunits required to recompose the image data unit are collected, theoutput unit 130 combines the stored transfer data units to recompose theimage data unit, and outputs an image according to the image data unitonto printing paper.

Note that an image data unit that is the last one to be read from thestorage unit 12 by the reading unit 21 as a transfer data unit may notalways have such a number of bytes that is determined by theaforementioned expression; thus, upon transmission of a transfer dataunit which is the last one to be transferred from the data transferapparatus 3, data units that do not contribute to image formation may betransmitted through some of the first to fifth lanes 201 to 205.

FIG. 5 is a diagram showing an example of lane mapping for when a540-byte transmit data unit where 28-byte control data units areappended to a 512-byte transfer data unit is transmitted assigned to thefirst to fifth lanes 201 to 205.

In the drawing, “STP” indicates the start frame 223 a shown in FIG. 3,“SEQ1” and “SEQ2” indicate the sequence number 222 a, and “Hd1” to“Hd16” indicate the header 221 a, which are the control data unit 220A.“D1” to “D512” indicate the transfer data unit 21 a. “ECRC1” to “ECRC4”indicate the ECRC 221 b, “LCRC1” to “LCRC4” indicate the LCRC 222 b, and“END” indicates the end frame 223 b, which are the control data unit220B.

The first part of a transmit data unit indicated by reference numeral1001 in FIG. 5 includes “STP”, “SEQ1”, “SEQ2”, “Hd1”, and “Hd2”. Thetransmitting unit 23 assigns “STP” to the first lane 201, and thereafterlikewise assigns “SEQ1” to the second lane 202, “SEQ2” to the third lane203, “Hd1” to the fourth lane 204, and “Hd2” to the fifth lane 205. Thetransmitting unit 23 performs transmission of these byte data units inparallel.

Subsequent to the transmission of the first part 1001 of the transmitdata unit, the transmitting unit 23 transmits the second part 1002(“Hd3” to “Hd7”) of the transmit data unit through the first to fifthlanes 201 to 205. Thereafter, likewise, the transmitting unit 23sequentially performs transmission of the third part 1003 (“Hd8” to“Hd12”) of the transmit data unit, the fourth part 1004 (“Hd13” to“Hd16” and “D1”) of the transmit data unit, and the fifth part 1005(“D2” to “DG”) of the transmit data unit.

By transmission of the 106th part 1106 (“D507” to “D511”) of thetransmit data unit and the 107th part 1107 (“D512” and “ECRC1” to“ECRC4”) of the transmit data unit, transmission of the 512-bytetransfer data unit 21 a and the ECRC 221 b is completed. By transmissionof the 108th part 1108 (“LCRC1” to “LCRC4” and “END”) of the transmitdata unit, transmission of the LCRC 222 b and the end frame 223 b iscompleted. As such, by 108 transmissions, transmission of all thetransmit data unit is completed and an unnecessary data unit is notincluded in any part of the transmit data unit for the respectivetransmissions.

FIG. 6 is a diagram showing a comparative example of lane mapping forwhen a transmit data unit including a 513-byte transfer data unit 21 bis transmitted through the first to fifth lanes 201 to 205.

The contents of the first to fifth parts 2001 to 2005 of a transmit dataunit and the contents of the 106th part 2106 of the transmit data unitin FIG. 6 are the same as the contents of the first to fifth parts 1001to 1005 of the transmit data unit and the contents of the 106th part1106 of the transmit data unit in FIG. 5; however, the 107th part 2107of the transmit data unit includes “D513” which is a transfer data unitof the 513th byte, and thus, the lanes to which subsequent parts of thetransmit data unit are assigned are shifted by one position. Then, theend frame “END” is assigned to the first lane 201 in the 109th part 2109of the transmit data unit, and “Pad” indicating an unnecessary data unit220C is assigned to the second to fifth lanes 202 to 205. As such, bythe increase of a transfer data unit by 1 byte, the number oftransmissions is increased by one, i.e., from 108 to 109.

Second Exemplary Embodiment

Next, a second exemplary embodiment of the present invention will bedescribed. In the first exemplary embodiment, description is made of thecase in which the number of lanes through which data units aretransmittable from the transmitting unit and the number of lanes throughwhich data units are receivable by the receiving unit are both five. Inthe present exemplary embodiment, on the other hand, the number of laneson the transmitting side differs from the number of lanes on thereceiving side. In the present exemplary embodiment, the image datacontrolling unit is configured to obtain information about the number oflanes on the receiving side and provide information about the smallerone of the numbers of lanes on the transmitting side and the receivingside to the reading unit. Therefore, even when an image forming unit ofa model with a different number of lanes is connected to the controller,by adjusting the number of bytes of a transfer data unit according tothe number of lanes through which data units are transmittable, thenumber of transmissions of unnecessary data units is reduced.

Third Exemplary Embodiment

Next, a third exemplary embodiment of the present invention will bedescribed. In the first exemplary embodiment, the case in which thenumber of lanes in the transmission channel is five is described. In thepresent exemplary embodiment, on the other hand, the number of lanes is4, 8, 12, 16, or 32. Even if the number of lanes is thus changed, atransfer data unit is computed according to the number of lanes and thusthe number of bytes of a transfer data unit that does not cause the needto transmit unnecessary data may be determined. Note that in the PCIExpress standard, 1, 2, 4, 8, 12, 16, and 32 lanes are defined.

Fourth Exemplary Embodiment

Next, a fourth exemplary embodiment of the present invention will bedescribed. Although in the above-described exemplary embodiments thenumber of bytes of a transfer data unit is computed based on the numberof lanes, in the present exemplary embodiment, the reading unit stores acorrespondence table between the number of lanes and a transfer dataunit, and determines the number of bytes of a transfer data unit basedon the correspondence table. Alternatively, the number of bytes of atransfer data unit may be specified by the image data controlling unit.

Other Exemplary Embodiments

Note that the present invention is not limited to the above-describedexemplary embodiments and may also be applied to, for example, systemsor apparatuses other than image forming systems. In addition, variousmodifications may be made in the present invention without changing thenature or the scope of the invention. For example, lanes that form atransmission channel are not limited to differential signal lines. Thetransmission channel may use an optical fiber, etc., or wirelesstransmission may be applied. In addition, the transmission channel isnot limited to those conforming to the PCI Express standard.

The foregoing description of the exemplary embodiment of the presentinvention has been provided for the purpose of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Obviously, many modificationsand various will be apparent to practitioners skilled in the art. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical application, therebyenabling other skilled in the art to understand the invention forvarious embodiments and with the various modifications as are suited tothe particular use contemplated. It is intended that the scope of theinvention be defined by the following claims and their equivalents.

What is claimed is:
 1. A data transfer apparatus comprising: atransmitting unit that transmits transmit data over a transmissionchannel having a plurality of lines, such that the transmit data areassigned to the plurality of lines by information unit of the transmitdata, the information unit including a plurality of pieces of bitinformation; a transmission controlling unit that appends control datato transfer data to be transferred to a receiving side to compose thetransmit data, the control data being for controlling transmission andreception of the transfer data; and a generating unit that obtainsinformation about the number of the lines in the transmission channel,that determines, based on the number of the lines and the number ofinformation units of the control data, the number of information unitsof the transfer data that makes the number of information units of thetransmit data integral multiple of the number of the lines, and thatgenerates transfer data of the determined number of information unitsfrom a part of the transfer data to be transferred to the receivingside.
 2. The data transfer apparatus according to claim 1, wherein thegenerating unit generates the transfer data by reading, chunk by chunk,a data unit of the number of information units corresponding to anumeric value, from a storage unit that stores the transfer data to betransferred to the receiving side, the numeric value being obtained bysubtracting the number of information units of the control data unitsfrom a numeric value which is an integral multiple of the number of thelines in the transmission channel.
 3. A data transmitting and receivingapparatus comprising: a transmission channel that has a plurality oflines; a transmitting unit that transmits transmit data over thetransmission channel, such that the transmit data are assigned to theplurality of lines by information unit of the transmit data, theinformation unit including a plurality of pieces of bit information; atransmission controlling unit that appends control data to transfer datato be transferred to a receiving side to compose the transmit data, thecontrol data being for controlling transmission and reception of thetransfer data; a generating unit that obtains information about thenumber of the lines in the transmission channel, that determines, basedon the number of the lines and the number of information units of thecontrol data, the number of information units of the transfer data thatmakes the number of information units of the transmit data integralmultiple of the number of the lines, and that generates transfer data ofthe determined number of information units from a part of the transferdata to be transferred to the receiving side; a receiving unit thatreceives the transmit data transmitted from the transmitting unit overthe transmission channel; and a reception controlling unit that extractsthe transfer data unit from the transmit data received by the receivingunit.
 4. An image forming apparatus comprising: a storage unit thatstores image data; a transmission channel that has a plurality of lines;a transmitting unit that transmits the image data as transmit data overthe transmission channel, such that the transmit data are assigned tothe plurality of lines by information unit of the transmit data, theinformation unit including a plurality of pieces of bit information; atransmission controlling unit that appends control data to transfer datato be transferred to a receiving side to compose the transmit data, thecontrol data being for controlling transmission and reception of thetransfer data; a generating unit that obtains information about thenumber of the lines in the transmission channel, that determines, basedon the number of the lines and the number of information units of thecontrol data, the number of information units of the transfer data thatmakes the number of information units of the transmit data integralmultiple of the number of the lines, and that generates transfer data ofthe determined number of information units from a part of the transferdata to be transferred to the receiving side; a receiving unit thatreceives the transmit data transmitted from the transmitting unit overthe transmission channel; a reception controlling unit that extracts thetransfer data from the transmit data received by the receiving unit; andan output unit that recombines the transfer data extracted by thereception controlling unit, to recompose the image data, and forms animage based on the image data.